The study population was the catchment population of Bellevue Hospital, a general hospital in lower Manhattan, New York City, with busy ambulatory care services that serve low income working communities. Cases and controls were recruited from among outpatients and inpatients at Bellevue Hospital and interviewed face-to-face or by telephone. Occupation, industry, and occupational exposures were determined by questionnaire supplemented by a Job Exposure Matrix. Odds ratios (ORs) of association between asthma and specific industrial, occupational, and exposure categories, controlled for major confounders, were estimated. The ORs were used to calculate occupation- and industry-specific Attributable Fractions, and an overall Population Attributable Fraction of asthma attributable to occupational factors. New onset occupational asthma and work-aggravated asthma were investigated separately.